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J. D. O'SHEA

Summary.

The duration of pseudopregnancy in rats was increased to 15·9±3·4 days (control 12·5 ±0·7) following surgical separation of the posterior parts of the uterine horns from their cervical attachments. Under these conditions, the uterine horns became distended with fluid. The uterine walls were stretched and thin, but appeared otherwise undamaged.

Deciduoma formation was readily induced in distended horns but the presence of deciduomata did not further prolong the duration of pseudopregnancy.

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J. D. O'SHEA

Summary.

Transection of the uterine horns near to their cervical ends (posterior uterine section) led to a prolongation of pseudopregnancy from 13·1±0·16 (control) to 14·9 ± 0·24 days (P<0·001). This was significantly greater than the prolongation following transection of the uterine horns one third of the way from the uterotubal junction to the uterine bifurcation (14·0 ± 0·16 days, P<0·01).

When unilateral ovariectomy was accompanied by contralateral posterior uterine section, the prolongation of pseudopregnancy (14·5± 0·20 days, control 12·8 ± 0·25 days, P< 0·001) was greater than when accompanied by ipsilateral posterior uterine section (13·7 ± 0·20 days, P<0·02).

These results indicate a quantitative and a unilateral component in the effects of uterine section, and support the hypothesis that prolongation of pseudopregnancy following posterior uterine section is brought about by the same mechanism as that following hysterectomy.

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J. D. O'SHEA

Summary.

When the posterior ends of the uterine horns in cycling female Hooded Wistar rats were transected, fluid accumulated in the uterine lumen. During pseudopregnancy, the mean volume of uterine fluid in these rats fell from 0·97±0·18 ml on Day 2 to 0·06±0·07 ml on Day 8 (P< 0·001). The volume remained low until the next onset of pro-oestrus.

Uterine fluid in normal rats at the time of oestrus contained 41·63± 3·99 mequiv./1 potassium, a higher level than that in blood plasma, and 2·07 ± 0·88 mg/ml total protein. Following transection of the uterine horns, the level of potassium remained high. The mean total protein concentration rose to three to thirteen times the normal value.

Transection of the uterine horns led to an increase in the mean duration of pseudopregnancy from 13·4±0·20 days to 15·2±0·33 days (P<0·001). When uterine fluid was withdrawn from transected horns during pseudopregnancy, the duration of pseudopregnancy was reduced to 14·3 ± 0·29 days (P<0·05). It is concluded that retention of uterine secretion is a causal factor in the prolongation of pseudopregnancy resulting from uterine transection.

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J. D. O'SHEA

Summary.

Mature ovarian follicles from three sheep were examined by electron microscopy. Many cells in the theca externa contained cytoplasmic filaments and dense bodies characteristic of smooth muscle cells. These observations suggest a contractile function in the theca externa.

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J. D. O'Shea and K. McCoy

Summary. Changes in luteal weight from about Day 20 to near term, and in quantitative histology as assessed by ultrastructural morphometry and light microscopic counts of mitosis and cell death on Days 30, 60, 100 and 142, were studied in 168 pregnant ewes.

Luteal weight (mean ± s.d.) remained constant at 0·56 ± 0·11 g until Day 120, and fell thereafter to reach 0·31 ± 0·11 g after Day 140 (P < 0·01). Up to Day 100, quantitative aspects of the composition of the luteal tissue showed no significant change, and values for volume density, cytoplasmic:nuclear ratio, cell number/mm3 and cell volume were comparable to values previously obtained for corpora lutea (CL) of the cycle. By Day 142 structural evidence of luteal regression was present, but regressive changes were much more marked in some CL than others. Mitosis was seen in a few cells (0·02–0·04%) on all of the days studied, but never in large luteal cells. Cell death was rarely seen up to Day 100, but had increased in incidence by Day 142 (P < 0·01). Luteal progesterone content, 55·2 ± 15·9 nmol/g on Day 30, was not significantly changed on Days 60, 100 or 142.

It is concluded that (1) structural regression of the CL of pregnancy does not begin until much later than the time (about Day 50) when pregnancy ceases to depend on the CL; (2) structural luteal regression begins before parturition, but its time of onset and/or rate of progression vary widely between animals; and (3) large and small luteal cells remain as distinctive populations throughout pregnancy, and their numbers at all stages can be accounted for by survival of the cells which differentiate during the genesis of the CL.

Keywords: corpus luteum; pregnancy; sheep; morphometry; luteal weight

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J. D. O'SHEA and C. S. LEE

Summary.

When two consecutive pseudopregnancies were induced in normal female Hooded Wistar rats, the duration of the second pseudopregnancy (12·6±0·18 days) was shorter than that of the first (13·2±0·20 days, P<0·05). This was associated with a shortening of vaginal oestrus in the second pseudopregnancy. The duration of the oestrous cycle following pseudopregnancy was also shorter than that of the cycle preceding pseudopregnancy (3·7±0·17 days versus 4·6±0·18 days, P<0·01).

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J. D. O'SHEA and C. S. LEE

Summary.

Two experiments were performed on female Hooded Wistar rats to determine the effects of section of utero-ovarian connections on the duration of pseudopregnancy.

Ligation and section of the anterior uterine blood vessels on Day 6 of pseudopregnancy caused a prolongation of the pseudopregnancy during which the operation was performed, and also of the subsequent pseudopregnancy (P<0·01). Neither section of the Fallopian tube nor that of the mesosalpinx and broad ligament significantly affected the duration of pseudopregnancy.

When the anterior uterine vessels were sectioned separately, it was shown that severing the artery led to a prolongation of pseudopregnancy (P<0·001). Section of the vein did not significantly affect the duration of pseudopregnancy.

These results suggest that the effects on pseudopregnancy of section of utero-ovarian connections depend primarily on interruption of the anterior uterine artery.

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J. D. O'Shea, R. J. Rodgers and P. J. Wright

Summary. Ovulation was induced by 3 × 30 μg LHRH i.v. at 90-min intervals in anoestrous Corriedale ewes. Plasma LH surges occurred in all of 31 ewes given LHRH, but ovulation occurred in only 16 of these ewes. Luteal weight and plasma progesterone concentration were lower in ewes in which ovulation was induced during anoestrus than in cyclic control ewes in the breeding season, and when data from induced and control ewes were pooled luteal weight was strongly correlated with plasma progesterone concentration (r = +0·612, P < 0·01). Five mature corpora lutea (CL) resulting from ovulation induced during anoestrus were compared by morphometric methods with 5 CL from cyclic control ewes. When data from induced and control CL were pooled, luteal volume was positively correlated with total number of cells per CL (r = + 0·869, P < 0·01) but negatively correlated with number of cells per mm3 luteal tissue (r = − 0·676, P < 0·05), i.e. smaller CL contained fewer cells, but more cells per unit volume. Relative numbers of large to small luteal cells, at ≅1:6, were similar in LHRH-induced and cyclic control CL. Large and small luteal cells were smaller in induced CL than in control CL, but cytoplasmic: nuclear ratio did not differ between induced and control CL. Basal and LH-stimulated progesterone production by dispersed luteal cells in vitro were lower for CL from LHRH-treated ewes than from controls. However, percentage increase in progesterone production in response to LH was not different between LHRH-treated and control ewes at any dose rate of LH used.

It is concluded that the small size of CL induced by LHRH is due primarily to the low numbers and small volumes of the luteal cells in these CL, and that subnormal luteal weight and subnormal progesterone production per luteal cell contribute to the low plasma progesterone concentrations in ewes treated with LHRH during seasonal anoestrus.

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R. J. Rodgers, J. D. O'Shea and J. K. Findlay

Summary. Corpora lutea from cyclic ewes were dissociated by collagenase digestion and trypsin/EGTA treatment. Enriched fractions of endothelial cells, small luteal cells and large luteal cells were prepared on a stepped gradient of Ficoll 400. Progesterone was measured by radioimmunoassay and the results corrected so that progesterone production by each cell type could be determined. Endothelial cells did not produce significant amounts of progesterone, with or without LH stimulation, and endothelial cell contamination of small and large luteal cell fractions did not influence progesterone production by these fractions. Mean ± s.e.m. basal progesterone production (n = 10) by large luteal cells was greater (P < 0·001) on a per cell basis than that by small luteal cells (1·16 ± 0·16 compared with 0·25 ± 0·06 pg/h/cell). However LH, which stimulated a maximal 3–4-fold increase in progesterone production by small luteal cells (LH ED50 = 0·14 ng/ml), had no significant effect on production by large luteal cells, when contamination by small luteal cells was taken into account. The response of small luteal cells was specific to LH, other hormones having had no significant effect.

Basal progesterone production by small luteal cells (0·12 ± 0·03 fg/h/μm3) calculated per unit volume of cell was not significantly different from that of large luteal cells (0·17 ± 0·02 fg/h/μm3). After LH stimulation, small luteal cells produced more progesterone than did large luteal cells (0·40 ± 0·09 compared with 0·18 ± 0·03 fg/h/μm3) (P < 0·05). When the amounts of progesterone produced per cell were multiplied by the absolute numbers of large luteal (1 × 107) and small luteal (5 x 107) cells in the intact corpus luteum, basal progesterone production by large luteal cells (11·6 ± 1·6 μg/h) was similar to that by small luteal cells (12·3 ± 3·0 μg/h). However, under LH stimulation, progesterone production by the small luteal cell type (39·9 ± 9·5 μg/h) was ∼ 3 times greater than that by the large luteal cell type (12·3 ± 1·6 μg/h) (P < 0·05).

We therefore conclude that small luteal cells may be the principal source of luteal progesterone production in the sheep.

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R. J. Rodgers, J. D. O'Shea and J. K. Findlay

Summary. Corpora lutea from cyclic ewes were dissociated by collagenase and trypsin/ EGTA treatments, and enriched fractions of small and large luteal cells were prepared on gradients of Ficoll. These fractions were incubated separately or remixed before incubation. Colchicine, cytochalasin B and the calcium channel-blocker verapamil significantly reduced progesterone production by both small and large luteal cell fractions, while isoprenaline stimulated an increase in progesterone production by large luteal cell fractions only. When fractions of small and large luteal cells were remixed, no more and no less progesterone was produced than would have been predicted from equivalent fractions incubated separately. There was therefore no evidence of synergism between small and large luteal cells in the production of progesterone. Prostaglandin F-2α, which can inhibit LH-stimulated progesterone production by ovine luteal tissue in vitro, had no effect on LH-stimulated progesterone production by small luteal cell fractions, but significantly inhibited that by enriched fractions of large luteal cells. Since large luteal cell fractions were contaminated with small luteal cells, which are probably responsible for the progesterone-secretory response of these fractions to LH, it was concluded that the inhibition of LH-stimulated progesterone production by small luteal cells is dependent on the presence of large luteal cells. Oxytocin added to large and small luteal cell fractions did not affect progesterone production by either fraction. It was therefore concluded that the inhibitory action of PGF-2α on LH-stimulated progesterone production may require the interaction of large and small luteal cells, but that oxytocin is not likely to be an intermediary in this interaction.